fix: C standard requires prototype (#805)

The latest compilers require all C functions to have a prototype to compile,
adds the void prototype to those functions requiring this

Author: dawesc

include/aws/cryptosdk/error.h

@@ -62,7 +62,7 @@ enum aws_cryptosdk_err {
  * Implicitly registers error strings for aws-c-common as well.
  */
 AWS_CRYPTOSDK_API
-void aws_cryptosdk_load_error_strings();
+void aws_cryptosdk_load_error_strings(void);
 
 #ifdef __cplusplus
 }

source/cipher.c

@@ -470,7 +470,7 @@ static int evp_gcm_encrypt_final(const struct aws_cryptosdk_alg_properties *prop
     return AWS_ERROR_SUCCESS;
 }
 
-static inline void flush_openssl_errors() {
+static inline void flush_openssl_errors(void) {
     while (ERR_get_error() != 0) {
     }
 }

source/error.c

@@ -39,6 +39,6 @@ static const struct aws_error_info error_info[] = {
 static const struct aws_error_info_list error_info_list = { .error_list = error_info,
                                                             .count      = sizeof(error_info) / sizeof(error_info[0]) };
 
-void aws_cryptosdk_load_error_strings() {
+void aws_cryptosdk_load_error_strings(void) {
     aws_register_error_info(&error_info_list);
 }